Release of pituitary gonadotrophins GtH I and GtH II in the rainbow trout (Oncorhynchus mykiss): modulation by estradiol and catecholamines.
The present study focused on the role of catecholaminergic neurons and estrogens on the release of gonadotropins I and II in immature and early vitellogenic female rainbow trout. The ovariectomy-induced increase of GtH I blood levels (from about 10 to 15 ng/ml) was prevented in vitellogenic fish by E2 supplementation. E2 implantation of immature fish decreased blood GtH I levels (from about 6 to 1 ng/ml). Blood levels of GtH II were low (about 0.5 ng/ml) and not altered by ovariectomy and E2 treatment. These data demonstrate that estrogens exert a negative feedback on the release of GtH I in trout. A treatment with alpha-methyl-p-tyrosine (MPT), an inhibitor of catecholamine synthesis, increased blood GtH II levels of sham-operated vitellogenic fish and ovariectomized fish implanted with E2, but had no effects in ovariectomized fish. MPT did not modify blood GtH I levels in any experimental group. A treatment of E2-implanted immature or vitellogenic fish with the dopamine antagonist pimozide also increased blood GtH II levels, but did not significantly change blood GtH I levels. These data demonstrate that release of GtH II, but not of GtH I, depends on an E2-activated DA inhibitory tone.
Saligaut
C
C
Campus de Beaulieu, U.A. INRA, Rennes cedex, 35042, France.
Linard
B
B
Mañanos
E L
EL
Kah
O
O
Breton
B
B
Govoroun
M
M
D000818:Animals; D002395:Catecholamines / Q000502:physiology*; D004298:Dopamine / Q000502:physiology; D004958:Estradiol / Q000502:physiology*; D005260:Female; D006065:Gonadotropins, Pituitary / Q000378:metabolism*; D017686:Oncorhynchus mykiss / Q000502:physiology*; D010868:Pimozide / Q000494:pharmacology; D014818:Vitellogenesis / Q000187:drug effects; D019805:alpha-Methyltyrosine / Q000494:pharmacology
D002395:Catecholamines; D006065:Gonadotropins, Pituitary; C057763:gonadotropin- pituitary, beta-subunit I, salmon; D010868:Pimozide; D004958:Estradiol; D019805:alpha-Methyltyrosine; D004298:Dopamine